The small and impoverished Central Africa nation has been unstable since 2015, when Nkurunziza decided to seek a third term in office that his opponents said was unconstitutional.
The referendum will decide whether to amend the constitution to extend presidential terms to seven years from five.
The proposed changes would limit the president to two consecutive terms but would not take into account previous terms, potentially extending Nkurunziza’s rule to 2034.
“The draft constitution submitted to the referendum will be adopted if the absolute majority of votes or fifty percent plus one vote, approve it,” Nkurunziza said in a statement issued by his office announcing the date.
Several leaders around Africa have sought to void laws or use other tactics to thwart opponents and prolong their reigns beyond constitutional limits, sometimes for decades.
Those who opposed Nkurunziza’s third five-term launched an armed struggle against his government, and the resulting violence has left hundreds dead and forced at least 400,000 people into exile.
Regional efforts to find a peaceful resolution to the conflict have dragged on without results so far.
This month, the ruling CNDD-FDD decided to give Nkurunziza the title of “CNDD-FDD Party Visionary” after appraising his ideas and teachings.
The title has no specific role attached to it and appeared to be aimed at shoring up support for the president ahead of the referendum.